Determining Body Mass Index

What is body mass index?

Determining how much your adolescent should weigh is not a simple matter of looking at an insurance height-weight chart, but includes considering the amount of bone, muscle, and fat in his or her body. The amount of fat is the critical measurement.

A good indicator of how much fat your adolescent carries is the Body Mass Index (BMI). Although it is not a perfect measure, it gives a fairly accurate assessment of how much of your teen's body is composed of fat.

The formulas below apply to adults only. For children and adolescents ages 2 to 19 years, the BMI varies by age and sex. An additional step must be performed after the BMI has been determined using one of the formulas below: the BMI-for-age percentile is determined by comparing your teen's weight to that of other teens of the same age and sex.

In other words, by plotting your child's BMI value into the Centers for Disease Control and Prevention's BMI-for-age growth chart (located at www.cdc.gov/growthcharts/clinical_charts.htm), you can determine if your child is underweight, within normal range, overweight, or obese.

To calculate an adult's BMI using the English formula

BMI can be calculated using pounds and inches.

BMI = Weight in Pounds x 703(Height in Inches) x (Height in Inches)

Multiply your weight in pounds by 703.

Divide that answer by your height in inches.

Divide that answer by your height in inches again.

For example, a person who weighs 165 pounds and is 5 feet 4 inches tall has a BMI of 28.

165 lbs x 703 = 28(64 inches) x (64 inches)

To calculate an adult's BMI using the Metric formula

BMI can be calculated using kilograms and meters.

BMI = Weight in Kilograms(Height in Meters) x (Height in Meters)

Your weight in kilograms.

Divided by your height in meters.

Divide that answer by your height in meters again.

For example, a person who weighs 99.79 Kilograms and is 1.905 Meters tall has a BMI of 27.5.

99.79 Kg = 27.5(1.905 Meters) x (1.905 Meters)

A BMI between 25 to 29.9 is considered overweight. Anything over 30 is considered obese. Normal BMI is between 18.5 and 24.9.